1. Technical Field
This invention relates to galvanic cathodic protection of embedded steel in concrete and the like. Specifically, to sacrificial anodes electrically linked to the steel reinforcement.
2. Description of Prior Art
Prior art devices of this type have relied on sacrificial anodes to address the issue of steel reinforcement corrosion which can and will occur due to the inherent porous nature of the concrete in which it is embedded. Such corrosion occurs when the concrete becomes contaminated with, for example, chloride ions from structural exposure to nature and user applied salt or carbonation due to carbon dioxide penetration into the concrete and loosing therefore its protective alkalinity. Once this occurs, the reinforcement steel will corrode increasing its volume causing accelerated failures of the surrounding concrete structure. By the use of the electrically connected sacrificial anode connected to the reinforcement steel cathodic protection is achieved, reducing or eliminating the corrosion of the steel by making it the cathode of the electric chemical cell.
One of the issues encountered in such a galvanic cathodic protection assemblies using sacrificial anodes, such as zinc or aluminum, regardless of the application venue is the size proportion of the anode to the protected structure surface.
This dissimilar surface issue in inherent by the nature of the structure being protected and the viable limitation of fixed anode surface as a potential so matter. Since the anode and cathodic surface areas should be in equilibrium and if not the sacrificial anode is not able to provide enough polarization to the protected structure, although the current of the anode varies insignificantly and is referred to as “mixed potential theory” illustrated in FIGS. 5 and 6 of the drawings showing a graphic display of “potential E” and anode and cathode related to increase cathode area.
FIG. 5 is a graphic depicting basis when dissimilar metals are connected electrically in a solution, they are forced to adapt the same potential and not their “at rest” potential. This example illustrates iron Fe and zinc Zn connected in an electrolyte with iron being the cathode and zinc the anode with the corrosion potential given at the illustration of the anode and cathode reactions.
FIG. 6, however, illustrates the effect of changing the area of one electrode relation to the other with total current, not current density on the YX axis, as shown. This illustrates the increased cathode area in the corresponding intersection of the zinc to the iron as surface area increases.
It will be evident therefore that criticality of effectively increasing the surface of the anode is relevant to the efficiency and practicality in any galvanic cathodic protection system.
Galvanic cathodic protection using sacrificial anodes such as zinc and aluminum which have inherently negative electro chemical potentials establishes a passive protective current flow which is well known and understood in the art, see for example U.S. Pat. Nos. 4,435,263, 5,292,411, 6,022,469, 6,033,553, 6,165,346, 6,562,229, 6,572,760, 7,160,433 and 7,488,410.
In U.S. Pat. No. 4,435,263, a back fill composition for magnesium galvanic anodes is disclosed using calcium sulphite, bentonite and one compound from a group of sodium alkylates and sodium dialkyldithiocarbamates.
U.S. Pat. No. 5,292,411 is directed to a method of patching eroded concrete using a metal anode with an ionically conductive hydrogel attached to a portion of the anode being in elongated folded form.
U.S. Pat. No. 6,022,469 discloses a method by which a zinc or zinc alloyed anode is set in mortar that maintains a high PH to provide passivity of the zinc anode maintaining same in an electro chemical active state.
U.S. Pat. No. 6,033,533 discloses the most effective humectants, debquescent or hydroscopic chemicals, lithium, nitrate and lithium bromine respectively to maintain a galvanic sprayed anode in active state.
U.S. Pat. No. 6,165,346 also claims a use of deliquescent chemicals to enhance the performance of the galvanic anodes.
U.S. Pat. No. 6,562,229 is drawn to a louvered metal anode with an electrocatalytically active coating on a substrate.
U.S. Pat. No. 6,572,760 illustrated the use of deliquescent material bound into a porous anode body to maintain the anodes electro chemical active properties.
U.S. Pat. No. 7,160,433 claims a cathodic protection system in which zinc anode embedded in mortar in which a humectant is employed to impart high ionic conductivity.
Finally, U.S. Pat. No. 7,488,410 shows an anode assembly for cathodic protection using an anode covered with an ionically conductive material having an electro chemical activating agent configured to conform closely to the steel reinforcing bar in which it adjacently protects.